In the case of such diagnostic instruments, a standard handle with exchangeable storage batteries serves for supplying power to diagnostic instruments which can be fitted onto the handle. The storage batteries are predominantly nickel-cadmium cells (NiCd) or nickel-metal hydride cells (NiMH). The known disadvantages of the NiCd cells—memory effect, self-discharging, low volume capacity, toxic constituents—are partly avoided by the more advanced NiMH cells. The memory effect and the self-discharging are considerably reduced; the volume capacity is higher and the cells can be disposed of without environmental impact. It is advantageous that NiMH cells have virtually the same voltage as NiCd cells (about 1.25 V). For both types of cell there are simple protective devices for limiting the charging or discharging current. Since the dimensions of NiMH cells are also similar to those of NiCd cells, NiMH batteries can be produced in the same dimensions as NiCd batteries. Therefore, it is readily possible to convert standard handles of NiCd cells to NiMH cells.
Lithium-ion storage batteries (Li-ion) have much better properties: no memory effect, very high volume capacity, no self-discharging, low weight. It is disadvantageous that Li-ion batteries have so far required a complex electronic protective circuit, which prevents overshooting or undershooting of specific voltages and limits the charging or discharging current, since otherwise there is the risk of the battery being destroyed or exploding.
The protective circuit is usually already installed in the battery by the battery manufacturer. It is additionally necessary to provide in the device for which an Li-ion storage battery is intended (for example cell phone, laptop) further electronic devices, which are generally referred to by the term charge/discharge management and adapt the properties of the battery to the properties of the device.
A special handle for medical diagnostic instruments to be used for Li-ion batteries in which the electronic charge/discharge management is installed has already been developed. The advantage of the advanced storage battery technology is offset here by the disadvantage that, when a user converts his diagnostic instruments to Li-ion batteries, he additionally has to obtain a new handle, although he already has a handle, or usually a number of handles, for NiCd or NiMH batteries.